Add a yum provider

Here we add a yum provider which uses the yum python interface directly to
interact with yum.  This allows you to manage yum-based systems without needing
to install puppet.

To enable add `plugin.package.provider = yum` to your mcollective server.cfg.

This adds the testing as requested in the comments of https://github.com/puppetlabs/mcollective-package-agent/pull/3 and as such supercedes that pull request.